The field of the invention is electronic packaging materials.
Almost all electronic circuits require some form of packaging, which typically involves polymeric materials. In general, polymeric materials utilized in packaging applications must have a broad range of desirable physical properties. These properties include low coefficient of thermal expansion (CTE), thermal stability, high glass transition temperature, low moisture absorption, and adhesion to metal (Cu, Cr) and polymers. Further desirable properties include lasability, low dielectric constant, non flammability, resistance to solvents, acids, bases and other inorganics used in wet chemistry processing steps, as well as ease of processing, and low cost.
Many polymeric materials for packaging electronic circuits are known in the art, and can be categorized into various classes according to their chemical composition. For example, one class of polymeric materials comprises polyimides that are commonly found in fibers, coatings, and films. However, polyimides exhibit several drawbacks, including high moisture absorption, dimensional movement associated with moisture absorption, poor adhesion to some substrates, shrinkage at high temperatures, and a sidedness to films such that each side of the film may have very different properties.
In another class the polymeric materials comprise epoxy compounds. Polymeric materials made from epoxy compounds typically have a glass transition temperature of about 140xc2x0-220xc2x0 C. and generally exhibit a moisture absorption of about 1-4%. While relatively inexpensive, most epoxy-based packaging compounds generally require drying and/or heat stabilization steps to allow their use in high density interconnect applications. For example, styrene-maleic anhydride/epoxies often exhibit desirable electrical and moisture properties. However, such epoxies having glass transition temperatures above 230xc2x0 C. are generally difficult to manufacture, and frequently exhibit an undesirably high coefficient of thermal expansion.
In a further class the polymeric materials comprise polyarylenes. Polyarylenes are thermally stable polymers, but are often difficult to process due to relatively low solubility in common organic solvents. A number of different routes for the preparation of high molecular weight polyarylenes soluble in organic solvents have been proposed. In one route, as shown for example in U.S. Pat No. 5,227,457, Marrocco, III, M., et al. describe the introduction of solubilizing groups such as phenyls onto the polymeric chain. Unfortunately, the solubilizing groups may also render the resultant polymer sensitive to processing solvents. In another route, for example U.S. Pat. No. 5,334,668 to Tour, J., et al. crosslinkable polyphenylene compositions are prepared having a relatively low molecular weight initially, but form upon heating crosslinked polymers exhibiting increased solvent resistance. However, these compositions may have among other disadvantages insufficient gap filling properties.
In view of the problems of various prior art polymeric compounds for electronic packaging, phenylethynyl substituted aromatic polymeric materials have been developed. Phenylethynyl and acetylene substituted compounds are well known [High Performance Thermosets, ed. Shiow-Ching Lin and Eli M. Pearce, Hanser Publishers, New York, 1993, pg 221], and generally confer the advantage that they can be thermally induced to crosslink to form fused aromatic compounds. More advantageously, crosslinking of phenylethynyl and acetylene substituted aromatic polymeric materials can be performed in the complete absence of polar functionalities when carbon atoms in an aromatic compound are substituted with phenylethynyl groups. For example, in U.S. Pat. No. 4,730,032, Rossi et al. teach phenylethynyl functionalized aromatic compounds which crosslink in a temperature range of about 270-330xc2x0 C. In another example, phenylethynyl substituted polymers with relatively high glass transition temperatures have been developed [Polym. Prep., Am. Chem. Div., Polym. Div., 28(1), 67 (1987], and in a further example, WO 97/10193 to Dow Chemical Company, bis(o-diethynyl) monomers as shown in prior art FIG. 1 are described.
However, some problems still persist with phenylethynyl or acetylene substituted aromatic polymeric materials. First, a relatively high level of a palladium based catalyst is required which may lead to subsequent problems in purification. Second, in order to produce phenylethynyl substituted aromatic compounds such as bis(ortho-diphenylyethynyl) aromatic compounds, a multistep synthesis is typically required, disadvantageously increasing the cost of the synthesis. Third, because most of the phenylethynyl substituted aromatic compounds are designed for direct use on/with semiconductors (integrated circuit encapsulants), high thermal stability is required. However, high thermal stability often demands for non-halogenated products frequently resulting in arduous processes to insure the absence of halogens. Still further, crosslinked phenylethynyl substituted aromatic compounds tend to be brittle, and often require relatively high temperatures for complete curing.
In spite of various polymers having been developed for packaging of electronic circuits, almost all such polymers suffer from one or more disadvantages. Therefore, there is a need to provide compositions and methods for improved packaging substrates for packaging of electronic circuits.
The present invention is directed to compositions and methods for improved packaging substrates for packaging of electronic components. In one step, first and second precursors are provided having a backbone, and first and second ethynyl groups. In another step a crosslinker is provided having a first and a second reactive group. In a further step the crosslinker, the precursors, and a solvent are applied to a surface. In a still further step first and second ethynyl groups from first and second precursors are reacted with the first and second reactive group of the crosslinker in a carbon-carbon bond formation reaction, respectively, thereby crosslinking the first backbone with the second backbone. In yet a further step, the solvent is removed.
In one aspect of the inventive subject matter, the first and second precursor preferably comprise a phenyl group, and more preferably a phenylindane. The ethynyl groups of the first and second precursors preferably comprise an aryl group, more preferably is an arylethynyl group and most preferably is a phenylethynyl group. It is also preferred that first and second precursors are identical, at least in an oligomeric form, or that first and second precursors are covalently bound together via a bridging group.
In another aspect of the inventive subject matter the precursor further comprises an adhesion enhancer covalently bound to the backbone of the precursor. Also preferred is that the precursor comprises a halogen atom, and more preferred a bromine atom.
In a further aspect of the inventive subject matter a toughener, preferably a butadiene-type compound or acrylonitrile/butadiene-type compound, is added to the solvent containing the first and second precursor and crosslinker.
Various objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the invention, along with the accompanying drawings in which like numerals represent like components.